A door security device (10) is provided for effectively locking a door (22) that has been partially opened. The device (10) includes a base plate (12) that is screwed onto a door frame (14), a first hinge plate (16) that is connected to the base plate (12) at a first hinge joint (56), a second hinge plate (18) that is similarly connected to the first hinge plate (16) at a second hinge joint (64), and a door plate (20) that is mounted on the door (22) and which incorporates a pair of hinge ears (92 and 94) between which is received a uniquely shaped hinge tongue (90) that is present at the end of the second hinge plate (18). A latch pin (24) that is also uniquely shaped, is insertable, when the door (22) is in a closed position, into ear bores (104 and 106) and a tongue bore (102) that are present within the hinge ears (92 and 94) and hinge tongue (90) to form a third hinge joint (108). The shape of the hinge tongue (90) and the interaction thereof with a biasing ramp (96) lying between the hinge ears (92 and 94) is such that as the door (22) is opened and the hinge tongue (90) rotates, the ear bores (104 and 106) and tongue bore (102) are forced out of axial alignment. When this occurs, a narrow barrel portion (134) of the latch pin (24) still permits hinging action, while upper and lower stops (130 and 132) present on the latch pin (24) provide that the latch pin (24) is locked into place, thereby preventing removal of the latch pin (24) by an intruder.